DE 196 46 055 discloses an audio playback system comprising a reproducing device, a speaker system, and a signal-processing unit for improving the spatial experience to a listener by applying psycho-acoustic signal processing. Physical placement of a speaker system is assisted by processing the presented audio to e.g. compensate the speed of audio in air. The audio output from a source is processed with effects to trick the listening ears in believing that the presented audio is coming from a direction where no speaker is actually placed.
This type of audio processing to e.g. virtually expand the size of the room and/or virtually displace sounds is commonly used in conjunction with consumer-related media productions where the size of the room and/or the number of surrounding speakers are limited. The processed and imaged/mirrored audio does not necessarily reflect the actual placement of musical instruments as they were recorded, but mostly introduces a feel of another location i.e. a concert hall, a church, an outdoor scene, etc. To obtain information of the actual placement of the physically available speakers in a system it may, however, be necessary to provide a calibration procedure prior to processing the sound source to compensate room characteristics, etc. This calibration may comprise an impulse response for each of the available speakers, where the impulse response may comprise speaker-independent characteristics such as group delay and frequency response, etc.
In a special audio-optimized environment, e.g. a soundproofed chamber, such a method may be sufficient to obtain an acceptable impulse response to desirably render an audio signal.
However, in a real environment, such as a living room or a kitchen, etc., it is a very difficult challenge to obtain authentic impulse responses to accomplish trustworthiness by the listener due to room reverberations, background noise, placement of probe microphones etc. during the calibration procedure.
To process the audio optimally with respect to audio placement, it may not be necessary to inquire impulse responses for the speaker system. It may be necessary for the processing unit to know the exact placement of speakers and the listener for estimation of acceptable processing schemes.
The human ear tolerates a slight deviation in speaker placement, but it is not possible to convince a listener that a sound is coming from the left speaker, when it is actually being played from e.g. the right speaker. Therefore, to satisfy and convince a listener of a speaker placement, the speaker actually has to be placed relatively near the intended location of the sound.
For this sake, it may be convenient to physically place a speaker on a chosen spot and let this speaker play material that may be appropriate for this location.
For example, if a speaker playing music is placed close to a listener, the listener may observe a given level of sound. If the speaker is placed at a longer distance from the listener, the playing speaker must carry out more power to let the listener obtain the same sound level as when the speaker is placed closer to him.
An example of the use of a speaker system according to the present invention could be watching a concert on television where an organ is playing on the left and a guitar is playing on the right. Positioning an audio-presenting device on the left would present the sound of the organ, positioning the audio-presenting device on the right would otherwise present the sound of the guitar.
In a stereo system where a left and a right audio signal is represented but only one loudspeaker placed to the left of a listener is available, it may be desirable to only reproduce the left signal to avoid spatial confusion of the listener. Likewise, if the loudspeaker is placed in front of the listener, the reproduced audio may comprise an appropriate mix of the left and the right audio channel.
Likewise, this may also be the situation in a surround sound environment, where a number of loudspeakers (typically 4 to 6) are placed around the listener to generate a 3D-like sound image. The speaker location is essential to e.g. instrument placement and accurate mirroring of acoustic spaces for high precision sound positioning. Unless e.g. the rear speakers (the speakers positioned behind the listener) in a surround sound setup are placed exactly symmetrically relative to the listener, undesirable effects may be apparent such as e.g. non-uniform sound delay, sound coloration, wave interference, etc. In addition, if the front speakers in a surround sound environment are placed further apart from the user than the rear speakers, a front/rear balance control of e.g. an amplifier has to be adjusted to prevent the rear speakers from dominating the sound image. However, the sounds coming from the rear speakers still arrive first at the listener by way of the physically shorter distance. This disadvantage is typically disregarded in home theatre arrangements.
A speaker system according to the present invention provides users with a system that enables them to position speakers in a space relative to the current auditory content without troublesome speaker/amplifier adjustments.
For processing the audio according to the speaker placement, it is necessary for the sound system to identify the loudspeaker location. It may be difficult and sometimes even impossible for a user to enter the exact location of a loudspeaker. Therefore it may be advantageous if the sound system is able to automatically determine the speaker placement prior to signal processing.
With that, the user can add audio-presenting devices without having to enter any software-based set-up programs or adjusting any system setting. All the user has to do is position the speaker somewhere within the useful area and the processing unit will determine which auditory signals will be presented through the audio-presenting device.